Methods for Conducting a Subsea Well Intervention, and Related System, Assembly and Apparatus

ABSTRACT

A method for conducting a subsea well intervention at a subsea well, and a related system. In particular embodiments, an assembly is provided comprising a wireline drum pressure container unit, a lubricator package having a lock chamber tube enclosing a tool string and having at least one valve in a vertical bore, and a connector used to connect the assembly to a well control package on a well head of the well. In such an embodiment, the method can include displacing well fluid in a cavity between the valve of the lubricator package and a valve of the well control package, using a clean fluid, while the valve of the lubricator package is closed. The assembly can then be disconnected from said well control package at the connector and retrieved to the surface, whereby contamination of seawater due to disconnection can be reduced or minimized.

TECHNICAL FIELD

The present invention relates to well intervention, and in particular relates to methods for conducting a subsea well intervention and a related system, assembly and apparatus.

BACKGROUND

Well interventions can be required from time to time. In the oil and gas exploration and production industry, for example, interventions may be performed to facilitate producing petroleum fluids from a well. In this regard, a tool string comprising various tools may be deployed on a line, such as a wireline cable or a rope, fed into a wellbore and used to perform a well intervention operation in the well. In order to deploy a tool string into a subsea well, an assembly containing the tool string in a chamber can be connected to a well head at the seabed, allowing the tool string to access the wellbore. The tool string is moved out of the chamber and into the wellbore for performing the intervention. Afterwards, the assembly or parts thereof may typically be disconnected from the well head. Upon disconnection, residual well fluids including for example hydrocarbon fluids can remain in the assembly from the intervention operation. If appropriate measures are not taken, such well fluids may spill into the sea and cause undesired contamination.

Published patent applications WO2008/015387 and WO2001/025593 describe techniques which include displacing well fluids of a vessel used for storing and deploying tools during subsea well interventions.

In particular, WO2008/015387 describes purging fluid upward through a tool storage package and winch arrangement. Such a technique can involve substantial volumes of fluid to be displaced and associated infrastructure which can be complex, and/or may be substantial in size, capacity and/or cost.

Furthermore, there can be a need for avoiding contamination by well fluids such as when disconnecting equipment from a subsea well head, and for ensuring that components at the well and/or in the assembly have appropriate pressure integrity.

An object is to address various needs, and/or obviate or at least mitigate drawbacks or difficulties associated with the prior art.

SUMMARY OF THE INVENTION

In light of the above, according to a first aspect of the invention, there is provided a method for conducting a subsea well intervention at a subsea well, the subsea well comprising a subsea tree with a well adapter and a well control package comprising at least one valve in a bore, the method comprising the steps of:

(a) making up an assembly of a wireline drum pressure container unit arranged on a lubricator package with a lock chamber tube enclosing a tool string and having at least one valve in the bore and a connector;

(b) lowering said assembly to said well control package and connecting the assembly using said connector to the well control package;

(c) pressure testing between said valve of the well control package and said valve of the lubricator package;

(d) opening the valve of the lubricator package and the valve of the well control package;

(e) lowering said tool string into the well;

(f) conducting a well operation using said tool string in the well;

(g) retrieving said tool string from the well back into the lock chamber tube;

(h) closing the valve of the well control package;

(i) closing the valve of the lubricator package;

(j) further pressure testing between said valve of the well control package and said valve of the lubricator package;

(k) while the valve of the lubricator package is closed, displacing well fluid in a cavity between the valve of the lubricator package and the valve of the well control package;

(l) disconnecting said assembly comprising said lubricator package and said wireline drum pressure container unit from said well control package at said connector; and

(m) retrieving the disconnected assembly to the surface.

The wireline drum pressure container unit may comprise an enclosed traction winch.

The well fluid may be replaced by displacement fluid, e.g. clean fluid. The method may further comprise using a clean fluid bottle for local storage of the displacement fluid in the proximity of the subsea tree and a fluid transfer system to drive the fluid from the clean fluid bottle through the cavity to one of a collector bottle, the well, or a production fluid outlet.

The well control package may be connected to the lubricator package at surface, prior to performing steps (a) to (m).

Either or both of the valve of the well control package and the valve of the lubricator package, may be arranged for being capable of shearing a line attached to the tool string.

The method may further comprise, subsequently to step (k), receiving flushed-out well fluid in a collector bottle arranged on said lubricator package.

The bore may preferably be a vertical bore. The well may typically be a petroleum well.

According to a second aspect of the invention, there is provided a subsea well intervention system comprising:

-   -   an assembly of a wireline drum pressure container package on a         lubricator package on said well control package, said lubricator         package for holding on a wireline a tool string in a lock         chamber tube of the lubricator package, wherein the system is         arranged for running said assembly to a well adapter;     -   a connector for connecting and disconnecting said well control         package to and from said well adapter;     -   a first valve in said lubricator package;     -   a second valve in said well control package,     -   a connector between said first and second valves; and     -   a fluid transfer system arranged for displacing well fluid in a         cavity between the first and second valves while the first valve         is closed.

The system may further comprise a well adapter for installing on a subsea tree, where the well adapter may be arranged for receiving a well control package on top of the well adapter.

The system may further comprise a clean fluid bottle for local storage of non-polluting displacement fluid in proximity of the subsea tree.

Either or both of the first and second valves may be a ball valve.

The wireline drum pressure container package may comprise, within a pressure vessel connectable on top of said lubricator package:

-   -   a motor driven drum for said wireline and arranged for         maintaining a back tension on said wireline; and     -   a motor driven traction winch for lowering and hoisting said         line with said tool string in said lubricator and said well.

The well fluid may be displaced using a displacement fluid.

The displacement fluid may comprise seawater from a seawater inlet. The displacement fluid may comprise non-polluting fluid, e.g. non-polluting to seawater.

The well control package may have a vertical bore. The well control package may comprise a lower shear/seal valve and an isolation shear seal ball valve in the bore.

According to a third aspect of the invention there is provided an assembly for performing a subsea well intervention at a subsea well, the assembly being configured to be releasably connected to a well head via a connector, the assembly comprising a lubricator package for containing a tool string in a chamber thereof, and being configured for displacing well fluid from a cavity between the chamber and the well head for preventing pollution of the sea upon disconnection of the assembly, the cavity being isolated from the chamber.

The chamber may be defined inside a lock chamber tube. The assembly may further comprise a fluid transfer system for displacing the well fluid from the cavity. The lubricator package may comprise at least one valve. The valve may be arranged for isolating the chamber from the wellbore. The valve may be further arranged to isolate the cavity from the chamber. The well head may comprise at least one valve, e.g. within a well control package provided thereupon. The cavity may thus be isolated between the valve of the lubricator package and the valve of the well head or well control package. The connector may comprise first and second parts, which may be connectable together to form the connection between the assembly and the well head. The connector may thus be provided between the valve of the lubricator package and the valve of the well head or well control package.

According to a fourth aspect of the invention there is provided apparatus for use in performing a subsea well intervention at a subsea well, wherein an assembly is releasably connected to a well head via a connector, the assembly comprising a lubricator package for containing a tool string in a chamber thereof, the apparatus being configured to displace well fluid from a cavity between the chamber and the well head for preventing pollution of the sea upon disconnection of the assembly, the cavity being isolated from the chamber.

The apparatus may comprise a fluid transfer system.

According to a fifth aspect of the invention there is provided a method of performing a subsea well intervention, using the assembly of the third aspect or the apparatus of the fourth aspect.

The method may include any one or more of: connecting the assembly to the well head; isolating the chamber from the wellbore and/or from the cavity; displacing the well fluid from the cavity.

Any of the aspects of the invention may include further features as described in relation to any other aspect, wherever described herein. Features described in one embodiment may be combined in other embodiments. For example, a selected feature from a first embodiment that is compatible with the arrangement in a second embodiment may be employed, e.g. as an additional, alternative or optional feature, e.g. inserted or exchanged for a similar or like feature, in the second embodiment to perform (in the second embodiment) in the same or corresponding manner as it does in the first embodiment.

Embodiments of the invention can be advantageous in various ways as will be apparent from throughout the specification. An advantage associated with some embodiments is that displacement of fluids can be limited to a cavity between two rams.

DESCRIPTION AND DRAWINGS

There will now be described, by way of example only, embodiments of the invention with reference to the accompanying drawings, in which:

FIG. 1 is a representation of a well intervention system on a subsea wellhead according to an embodiment of the invention;

FIGS. 2 to 13 are representations showing in sequence steps in a method for conducting a well intervention according to an embodiment of the invention; and

FIG. 14 is a schematic representation showing the cavity from which well fluids are flushed out in the method of FIGS. 2 to 13.

With reference firstly to FIG. 1, a well intervention system 400 is shown. The system 400 has a winch package or line drum pressure container package 100, a lubricator package 80, and a well control package 30.

The line drum pressure container package 100 has a line drum pressure container unit 101 comprising a pressure vessel.

The lubricator package 80 includes the following:

-   -   a first valve in the form of an upper shear seal ball valve 83;     -   a lock chamber pipe 81;     -   a fluid transfer system 70;     -   a clean bottle 72 for flushing fluid;     -   a collector bottle 71 for well fluids;     -   a hydraulic power unit (HPU) 60; and     -   a second valve in the form of a lower shear seal ball valve 82.

The well control package 30 includes a third valve in the form of an isolation [shear seal] ball valve 34 and a fourth valve in the form of a lower shear seal [ball] valve 32.

As can be seen, the well head is at the seabed S and has a well adapter 10 arranged on a horizontal subsea “christmas” tree 1. The well adapter 10 is provided with a kill/flush line 2, and a crown plug 3 is installed.

The system 400 further includes an upper quick connector 102 comprising parts 102 a, 102 b connecting the line drum pressure container package 100 and the lubricator package 80. The system 400 further includes an upper quick connector 36 comprising parts 36 a, 36 b connecting the lubricator package 80 and the well control package 30. Furthermore, the system 400 further includes a lower quick-connector 11 comprising parts 11 a, 11 b connecting the well control package 30 to the well adapter 10. The system also has a pressure sensor 84.

The system 400 includes a tool string S1, S2 which in FIG. 1 is contained in the lock chamber pipe 81.

An assembly A includes the line drum pressure container package 100, the lubricator package 80, and the well control package 30. The line drum pressure container package 100 comprises the pressure vessel assembled and mounted on the lubricator package 80 which is connector-mounted on the well control package 30 with a further connection, together configured to be prepared with a tool string S1, S2 and lowered in the sea for connecting the assembly A to the well adapter 10 on the subsea wellhead. It can be noted that the first valve 83 between the pressure vessel and the lubricator package 80 may be a shear seal ball valve and is an optional feature.

FIG. 2 shows the assembly A, including the line drum pressure container package 100, the lubricator package 80, and the well control package 30 being lowered to the well adapter 10 on the subsea tree 1. In FIG. 2, a cavity 35 between the second valve 82 and the third valve 34 is indicated. The assembly A is being lowered using a handling wire 90. A first tool string S1 is housed and protected in the liquid-filled lubricator.

FIG. 3 illustrates the assembly A after being lowered onto the well adapter 10. The well control package 30 is connected to the well head with the crown plug 3 present, and pressure testing is performed. The well control package 30 is connected to the well adapter 10. The third valve 34 and the fourth valve 32 are open. The second, shear seal, valve 82 of the lubricator package 80 is closed. Pressure testing above the crown plug 3 is performed.

FIG. 4 shows the crown plug 3 being pulled, subsequent to the step shown in FIG. 3. The second valve 82 on the lubricator is open, and the tool string S1 is lowered to pull the crown plug 3.

FIG. 5 shows the crown plug 3 being retrieved to the lubricator, back into the lock chamber pipe 81, in a further step. The fourth valve 32 [i.e. the lower shear/seal valve] is closed, and the second valve 82 [i.e. the lubricator valve], is closed. The third valve 34 is open. The region between the fourth valve 32 and the second valve 82 [i.e. between the lower shear/seal valve and the lubricator valve] is bled off, and the fourth valve 32 [i.e. lower shear/seal valve] is pressure tested. A pressure sensor 84 in the second valve 82 is provided for sensing pressure in a region between the second valve 82 and the third valve 34 in the cavity 35. The crown plug 3 is retrieved from its position in FIG. 4 by a distance D.

FIG. 6 shows a next step in which the cavity 35 is being flushed by a clean fluid F1C from the clean bottle 72. Flushed fluid in the form of well fluid F1P is collected in the collector bottle 71. This will allow disconnection of the second valve 82 from the third valve 34 because the cavity fluid becomes clean and thus environmentally friendly. The third valve 34 is closed. A pressure test between the second valve 82 and the third valve 34 is performed. The cavity 35 is then flushed with an environmentally friendly fluid, between the second and third valves 82, 34.

In other embodiments, the clean fluid F1C may be provided from the surface or from seawater from the surrounding sea.

In FIG. 7 a part of the assembly A is disconnected from the well control package 30. The disconnected part of the assembly, assembly A′, includes the lubricator package 80 and the line drum pressure container package 100. The assembly A′ is shown with the crown plug 3 on its way for being retrieved to the surface. The well control package 30 is shown with two valves closed forming a pressure tested barrier on the well adapter 10. The lubricator package 80 is disconnected from the well control package 30. The second, third and fourth valves 82, 34 and 32 are closed. The lubricator package 80 and line drum pressure container package 100 are retrieved upward to the surface, as indicated by arrow U.

In FIG. 8, a subsequent step is shown in which the assembly A′, which was retrieved to the surface, has been prepared with a new tool string S2 for operating in the well. In FIG. 8, the assembly A′ is lowered as indicated by arrow L. The new tool string S2 is installed in the lock chamber pipe 81 in the lubricator and a pressure test performed at the surface. The line drum pressure container package 100 and the lubricator package 80, including the new tool string S2 are run, toward the seabed S. The second, third and fourth valves 82, 34, 32 are closed. The well control package 30 is arranged on the well adapter 10 as in the preceding step of FIG. 7. The clean fluid bottle 72 contains clean fluid F1C for flushing the cavity 35.

In one variant, the step illustrated in FIG. 8 can be performed using a new assembly which is configured in the same way as the assembly A′. Thus, other variants of the method are possible where this step makes use of a new assembly which may not have previously been used in the method.

In other embodiments, FIG. 8 may also be illustrative of a first step of a method for conducting subsea well intervention when a well control package 30 is already installed on the well adapter 10 on the subsea tree 1 prior to commencement.

In FIG. 9, a yet further step is shown in which the lubricator package 80 containing the new tool string S2 is being connected to the well control package 30. The third valve, isolation valve 34 and the second valve, lubricator valve 82 are pressure tested. Accordingly, pressure testing between the second and third valves 82, 34 may be performed. The second, third and fourth valves 82, 34, 32 are closed.

FIG. 10 shows a further step in which the third valve, isolation valve 34 is opened and in-flow testing of the fourth valve, shear-seal valve 32 is conducted. In doing so, the second valve 82 is closed, the third valve 34 is open, and the fourth valve 32 is closed.

FIG. 11 shows a further step in which the fourth valve, shear-seal valve 32 is opened, the second valve, lubricator valve 82 is opened, and the tool string S2 is lowered into the well as indicated by arrow R and used for conducting a mechanical, chemical or logging operation in the well. The wireline W from the drum to the logging string S2 may be a rope-like wireline with a very small allowable bending radius, as described in patent publication WO2013/036145. In FIG. 11, the second, third and fourth valves 82, 34, 32 are all open.

FIG. 12 illustrates the tool string S2 in a further step retrieved back to the lock chamber pipe 81 in the lubricator and with the lower valve 82 of the lubricator package 80 closed. Similar preparations as above may be taken to test valves and clean the cavity 35 before disconnecting the lubricator package 80 from the well control package 30. The well control package 30 may be left residing on the wellhead adapter 10 for subsequent installation of a crown plug 3 or a subsequent well intervention. The second valve 82 is closed, the third valve 34 is closed and the fourth valve 32 is closed. A bleed off is performed, between the second valve 82 and the fourth valve 32. The fourth valve 32 is inflow tested. The cavity 35 between the second and third valves 82, 34 is flushed clean by non-polluting clean fluid F1C below the second valve, and flushed well fluids F1P are retained in the collector bottle 71. The lubricator package 80 is then disconnected non-pollutingly from the well control package 30.

FIG. 13 illustrates the disconnected assembly A′ including the line drum pressure container package 100 [including unit 101] and the lubricator package 80 being retrieved to the surface as indicated by arrow U′. The tool string S2 is retrieved in the lock chamber tube 81 of the lubricator package 80, the lower shear-seal valve 32 and lubricator valve 82 have been closed and bled off. The fourth valve, shear seal valve 32 has been in-flow tested, third valve, isolation valve 34 is closed, cavity 35 has been flushed with non-polluting fluid F1C, and flushed well fluid F1P has been collected in collector bottle 71. Lubricator package 80 has been disconnected from well control package 30 to obtain non-polluting disconnection. No well fluid is spilt into the seawater.

With reference to FIG. 14, the cavity 35 is shown between the second and third valves 82, 34 when first and second parts of connector 36 a, 36 b are connected. Clean fluid F1C is supplied from the bottle 72 through inlet 73 into the cavity 35, and flushed well fluid F1P in the cavity 35 is flushed out of the cavity 35 through an outlet 74 to the collector bottle 71. In other variants, a seawater inlet may provide a supply of seawater from the sea through the inlet 73 to flush out the cavity 35, instead of from the bottle 72.

It is important in subsea well intervention operations to ensure that there are always two pressure barriers between the well and the sea. In addition, it is important to test these barriers when established, before conducting a subsequent operation. Furthermore, it is important to avoid polluting the sea when disconnecting valve packages for retrieving them to the surface. Such precautions can prevent leakage and pollution in case one barrier should fail by accident.

In an embodiment of the invention, with reference again to the FIGS. 1 to 14, a method for conducting an intervention of subsea petroleum wells comprises utilizing a well adapter 10, a well control package 30, a lubricator package 80 and a winch package 100 comprising the line drum pressure container unit 101. These are installed on the subsea tree 1. The well adapter 10 is an interface between the subsea tree 1 and the well control package 30 and may include hydraulic and electrical features in addition to the mechanical features. The well control package 30 is equipped with at least one valve 32, 34 in a vertical bore. Additional valves can preferably be added for increased versatility and reliability. The lubricator package 80 is likewise equipped with at least one valve 82 in the vertical bore, a lock chamber pipe 81 and a fluid transfer system 70. The lock chamber pipe 81 acts as a deployment chamber for the tool string S1, S2 during the start and end of the operation. The fluid transfer system 70 may be used for two purposes, a first purpose being to displace the fluids in the cavity 35 between the closed valves 82, 34 of the lubricator package and the well control package respectively, and a second purpose being used to verify the integrity of the system. The lubricator package 80 can also have a valve 83 in the vertical bore above the lock chamber pipe 81 which will be redundant to the valves further below and constitute a backup in case these are blocked by the tool string S1, S2.

The subsea well intervention method starts by assembling the winch package 100 and the lubricator package 80 that enclose the first tool string S1. The tool string S1 is attached to the lower end of the line spooled on the winch drum. Said assembly 100, 80 is lowered to the well control package 30 installed on the subsea tree 1 by means of the well adapter 10, and is then connected 36 a, 36 b (see e.g. FIG. 8).

In an embodiment of the invention the pressure integrity of the aforementioned connection (36 a, 36 b) is validated by using the fluid transfer system 70 to generate a monitored over-pressure in the cavity 35 between the lowermost valve 82 of the lubricator package 80 and the uppermost valve 34 of the well control package (see e.g. FIG. 9 and related description above).

Proceeding further, all of the valves of the lubricator package 80 and of the well control package 30 are opened. This may be done in a manner with consecutive integrity checks of each step (see e.g. FIG. 10 and related description above).

When the pressure integrity has been confirmed throughout and the valves 82, 32, 34 are open, the tool string S1 is then lowered into the well (see e.g. FIGS. 10 and 11 and related description above) by lowering using the winch in the line drum pressure container unit 101. The tool string S1 is then used to conduct a well intervention inside the well before at least a part of it is retrieved back up into the lock chamber tube 81 and the valves 82 of the lubricator package 80 and the valves 32, 34 of the well control package 30 are closed.

The tool string comprises elements which are mechanical, electrical, radiating, explosive, or optical or any combination of these. The tool string can be used to activate actions or passively monitor the conditions of the well. It may also include driven machinery such as well tractors and/or milling tools.

The fluid transfer system 70 is used to validate the pressure integrity of the said closed valves 82 of the lubricator package 80 and the valves 32, 34 of the well control package 30, and to displace the fluids in the cavity 35 between the two said valves 82, 34. The displacement of fluids replaces the potentially polluting well fluid trapped in the cavity 35 by a non-polluting fluid (see e.g. FIG. 12 and related description above).

The assembly 100, 80 of the lubricator package 80 and winch package 100 can then be disconnected from the well control package 30 at the said connection 36 a, 36 b and retrieved to surface without spilling any potentially polluting or harmful fluids to the sea (see e.g. FIG. 13). The aforementioned method can be repeated with the same or other tool strings for various well intervention tools for intervention operations according to the operator's desire.

In an embodiment of the invention, the winch package 100 comprises a traction winch 102 and a drum, enclosed inside a pressure container unit 101. Such a line drum pressure container arrangement is exemplified by patent publication WO2013/036145.

In an embodiment of the invention, the fluid transfer system 70 comprises a clean fluid bottle 72 for local storage of the non-polluting displacement fluid in the proximity of the subsea tree 1. Said vessel is preferably used to bring the non-polluting displacement fluid from the surface to the seabed and thus eliminates the need for a dedicated fluid line from the surface. The displacement of fluids from the cavity 35 between the two valves 82, 32 is performed by driving non-polluting displacement fluid held from the clean fluid bottle 71 through the cavity 35 to either a collector bottle 71, into the well or to a production fluid outlet. The driving mechanism for displacing the displacement fluid can be a piston, a pump, utilizing differential pressure, or a combination of these. The driving mechanism intended for driving the displacement fluid can secondarily be used for integrity testing by generating a controlled over-pressure.

In an embodiment of the invention, the well control package 30 is installed on the well adapter 10 on the subsea tree 1 prior to commencing the method as seen in FIG. 8.

In an embodiment of the invention, the well control package 30 is installed to the lubricator package 80 at surface, prior to the commencement of the method, as seen in FIG. 2. The subsequent steps of the method are then adapted accordingly. The well adapter may be an integral part of either the well control package 30 or the subsea tree 1.

In an embodiment of the invention at least one of the valves 32, 34 of the well control package 30 and/or the valve 82 of the lubricator package is arranged for being capable of shearing the line W attached to the tool string S1 and/or the tool string S1 itself.

In an embodiment of the invention at least one of valve 32 and valve 82 of the lubricator package 80 is a ball valve.

Various modifications and improvements may be made without departing from the scope of the invention herein described.

Various other aspects or embodiments of the invention are set out in the following numbered paragraphs:

-   -   1. A method for conducting a subsea well intervention, said         subsea well comprising a subsea tree (1) with a well adapter         (10) and a well control package (30) comprising at least one         valve (32) in the vertical bore); (FIG. 8) comprising the steps         of:     -   making up an assembly (100, 80) of a wireline drum pressure         container unit (100, 101) arranged on a lubricator package (80)         with a lock chamber tube (81) enclosing a tool string (s2) and         having at least one valve (82) in the bore and a connector (36         a, b);     -   lowering said assembly (100, 80) to said well control package         (30) and connecting it using said connector (36 a, b) to said         well control package (30); (FIG. 9)     -   pressure testing between said well control package's (30) valve         (32) and said lubricator's valve (82), (FIG. 9);     -   opening said lubricator package's (80) valve (82) and the well         control package's (30) one or more valves (32, 34); (FIG. 10)     -   lowering said tool string (S2) into the well; (FIG. 11)     -   conducting a well operation using said tool string (s2) in the         well, (FIG. 11)     -   retrieving said tool string (S2) from the well back into the         lock chamber tube (81), (FIG. 12);     -   closing said well control package's (30) one or more valves (32,         34);     -   closing said lubricator package's (80) valve (82);     -   pressure testing between said well control package's (30) valve         (32) and said lubricator package's (80) valve (82);     -   displacing the well fluids in the cavity (35) between the two         said valves (82 and 32) with a non-polluting fluid (F1C)         [non-polluting to seawater]     -   disconnecting said assembly (100, 80) comprising said lubricator         package (80) and said wireline drum pressure container unit         (100, 101) from said well control package (30) at said connector         (36 a, b), and retrieving them to the surface.     -   2. A method according to paragraph 1, wherein said wireline drum         pressure container unit (100, 101) comprises an enclosed         traction [capstan] winch.     -   3. A method according to paragraph 1 or 2, using a clean fluid         bottle (72) for local storage of the non-polluting displacement         fluid (F1C) in the proximity of the subsea tree (1) and a fluid         transfer system (70) to drive the non-polluting fluid from the         clean fluid bottle (72) through the cavity (35) to either a         collector bottle (71), into the well or to a production fluid         outlet.     -   4. The method according to any of paragraphs 1 to 3 wherein the         well control package (30) is installed to the lubricator package         (80) at surface, prior to the commencement of the method.     -   5. The method according to any of paragraphs 1 to 4 wherein at         least one of the said well control package's valve (32) or         lubricator package's valve (82) is arranged for being capable of         shearing the line attached to the tool string.     -   6. The method according to any of paragraphs 1 to 5, subsequent         to displacing the well fluids in the cavity (35) between the two         said valves (82 and 32) with a non-polluting fluid (F1C)         [non-polluting to seawater], retaining flushed-out well fluid         (F1P) to a collector bottle (71) arranged on said lubricator         package (80).     -   7. A subsea well intervention system comprising:     -   an assembly (100, 80, 30) of a wireline drum pressure container         package (100, 101) on a lubricator package (80) on said well         control package (30), said lubricator package (80) for holding         on a wireline a tool string (S1, S2) in its lock chamber tube         (81), and arranged for running said assembly (100, 80, 30) to a         well adapter (10) (FIG. 2) and comprising a connector (11) for         connecting and disconnecting said well control package (30) to         and from said well adapter (10) (FIG. 3),     -   a first valve [e.g. lower shear seal ball valve (82)] in said         lubricator package (80),     -   a second valve [e.g. isolation shear seal ball valve (32)] in         said well control package (30),     -   a connector (36) between said first valve and said second valve,     -   a fluid transfer system (70) arranged for displacing the well         fluids in the cavity (35) between the said first valve and said         second valve     -   8. The device according to paragraph 7, comprising a well         adapter (10) for installing on a subsea tree (1), said well         adapter (10) arranged for receiving a well control package (30)         on top of it, (FIG. 2),     -   9. The device according to paragraph 7 or 8 wherein said fluid         transfer system (70) comprising a clean fluid bottle (72) for         local storage of the non-polluting displacement fluid (F1C) in         the proximity of the subsea tree (1)     -   10. The device according to paragraph 7, 8 or 9 wherein at least         one of the said well control package's (30) valve or lubricator         package's (80) valve is a ball valve.     -   11. The device according to any of paragraphs 7 to 10, wherein         said wireline drum pressure container package (100, 101)         comprises     -   a motor driven drum for said wireline and arranged for         maintaining a back tension on said wireline,     -   a motor driven traction [capstan] winch for lowering and         hoisting said line with said tool string (S1, S2) in said         lubricator and said well,     -   all within a pressure vessel connectable on top of said         lubricator package (80).     -   12. The device according to any of paragraphs 7 to 11, wherein         said non-polluting displacement fluid (F1C) is constituted by         seawater (F1C) from a seawater inlet (72).     -   13. The device according to any of paragraphs 7 to 12, said well         control package (30) comprising in addition to said at least one         valve (32) in the vertical bore, a lower shear/seal valve (32)         and optionally an isolation shear seal ball valve (34). 

1. A method for conducting a subsea well intervention at a subsea well, the subsea well comprising a subsea tree with a well adapter and a well control package comprising at least one valve in a bore, the method comprising the steps of: (a) making up an assembly of a wireline drum pressure container unit arranged on a lubricator package with a lock chamber tube enclosing a tool string and having at least one valve in the vertical bore and a connector; (b) lowering said assembly to said well control package and connecting the assembly using said connector to the well control package; (c) pressure testing between said valve of the well control package and said valve of the lubricator package; (d) opening the valve of the lubricator package and the valve of the well control package; (e) lowering said tool string into the well; (f) conducting a well operation using said tool string in the well; (g) retrieving said tool string from the well back into the lock chamber tube; (h) closing the valve of the well control package; (i) closing the valve of the lubricator package; (j) further pressure testing between said valve of the well control package and said valve of the lubricator package; (k) while the valve of the lubricator package is closed, displacing well fluid in a cavity between the valve of the lubricator package and the valve of the well control package; (l) disconnecting said assembly comprising said lubricator package and said wireline drum pressure container unit from said well control package at said connector; and (m) retrieving the disconnected assembly to the surface.
 2. The method of claim 1, wherein the wireline drum pressure container unit comprises an enclosed traction winch.
 3. The method of claim 1, which further comprises using a clean fluid bottle for local storage of the displacement fluid in the proximity of the subsea tree and a fluid transfer system to drive the fluid from the clean fluid bottle through the cavity to one of a collector bottle, the well, or a production fluid outlet.
 4. The method of claim 1, wherein the well control package is connected to the lubricator package at surface, prior to performing steps (a) to (m).
 5. The method of claim 1, wherein either or both of the valve of the well control package, and the valve of the lubricator package, is arranged for being capable of shearing a line attached to the tool string.
 6. The method of claim 1, which further comprises, subsequently to step (k), receiving flushed-out well fluid in a collector bottle arranged on said lubricator package.
 7. A subsea well intervention system comprising: an assembly of a wireline drum pressure container package on a lubricator package on said well control package, said lubricator package for holding on a wireline a tool string in a lock chamber tube of the lubricator package, wherein the system is arranged for running said assembly to a well adapter; a connector for connecting and disconnecting said well control package to and from said well adapter; a first valve in said lubricator package; a second valve in said well control package, a connector between said first and second valves; and a fluid transfer system arranged for displacing well fluid in a cavity between the first and second valves while the first valve is closed.
 8. The system of claim 7, further comprising a well adapter for installing on a subsea tree, the well adapter being arranged for receiving a well control package on top of the well adapter.
 9. The system of claim 7, further comprising a clean fluid bottle for local storage of non-polluting displacement fluid in proximity of the subsea tree.
 10. The system of claim 7, wherein either or both of the first and second valves is a ball valve.
 11. The system of claim 7, wherein said wireline drum pressure container package comprises, within a pressure vessel connectable on top of said lubricator package: a motor driven drum for said wireline and arranged for maintaining a back tension on said wireline; and a motor driven traction winch for lowering and hoisting said line with said tool string in said lubricator and said well.
 12. The system of claim 7, wherein the well fluid is displaced using a displacement fluid (F1C).
 13. The system of claim 12, wherein the displacement fluid comprises seawater from a seawater inlet (72).
 14. The system of claim 7, wherein said well control package has a vertical bore and comprises a lower shear/seal valve and an isolation shear seal ball valve in the vertical bore.
 15. An assembly for performing a subsea well intervention at a subsea well, the assembly being configured to be releasably connected to a well head via a connector, the assembly comprising a lubricator package for containing a tool string in a chamber thereof, and being configured for displacing well fluid from a cavity between the chamber and the well head for preventing pollution of the sea upon disconnection of the assembly, the cavity being isolated from the chamber.
 16. Apparatus for use in performing a subsea well intervention at a subsea well, wherein an assembly is releasably connected to a well head via a connector, the assembly comprising a lubricator package for containing a tool string in a chamber thereof, the apparatus being configured to displace well fluid from a cavity between the chamber and the well head for preventing pollution of the sea upon disconnection of the assembly, the cavity being isolated from the chamber.
 17. (canceled) 